Saturn's Moon- Titan
Titan, a world in itself, is the largest moon of Saturn and therefore the second largest moon in our system. Being the sole moon within the solar system with a considerable atmosphere and being one of the Earth like world that has standing bodies of liquid, including rivers, lakes and seas, on its surface, makes Titan the most important moon of Saturn.
Titan alone makes up to 96% of the mass of all the moons including Saturn’s rings. Not only is Titan the foremost important moon of Saturn, it is also the only moon within the solar system with a substantial atmosphere. Bigger than Earth's moon, and larger than even the planet Mercury, it has a radius of about 1,600 miles. It is about 9.5 AU from the sun. Light from the Sun takes about 80 minutes to reach Titan; due to which, sunlight is about 100 times fainter at Saturn and Titan than at Earth.
Titan’s atmosphere is mostly nitrogen and a small amount of methane. It is known to have a cycle of liquids raining from clouds, flowing across its surface, filling lakes and seas, and evaporating back into the sky just like earth. Titan takes 15 days and 22 hours to finish a full orbit around Saturn. It always shows the same face to the planet as it orbits because it is tidally locked in synchronous rotation with Saturn. Since Titan orbits roughly along Saturn’s equatorial plane, and its tilt relative to the sun is similar to that of Saturn’s, the seasons on the moon are on an equivalent schedule as Saturn’s.
Titans internal structure remains a mystery but we can infer that it has five primary layers based on the data from the Cassini-Huygens mission. The inner most layer being a core of rock (specifically water-bearing silicate rock), which is surrounded by a shell of water ice i.e., ice-Vl. Ice-Vl is surrounded by a layer of salty liquid water. The outer most crust may be a layer of water ice. And the surface is covered by a dense atmosphere.
Origin of Titan also remains a mystery though its atmosphere does provide a clue. Isotope’s nitrogen-14 and nitrogen-15 were measured in Titan’s atmosphere by several instruments on the NASA and ESA Cassini-Huygens mission. Instruments have also detected that Titan’s nitrogen isotope ratio is very similar to that found in comets from the Oort Cloud. Titan’s atmospheric nitrogen ratio suggests that it was formed early within the solar system's history, within the proto solar nebula, instead of forming in the Saturn’s sub-nebula. Within the solar system Titan’s surface is one among the foremost Earth like places, albeit at vastly colder temperatures and with different chemistry. It is so cold i.e., about -290 degrees Fahrenheit that water ice plays the role of rock. Titan may have volcanic activity also, but with liquid water “lava” rather than molten rock. Titan’s surface is carved by flowing methane and ethane, which carves river channels and fills them with liquid gas. No other world within the system, apart from Earth, has that sort of liquid activity on its surface.
Vast regions of dark dunes stretch across the equatorial region of Titan’s landscape, which contains prominent impact craters. Earth too has craters which are erased by the relentless forces of flowing liquid, wind, and the recycling of the crust via plate tectonics. These forces are present on Titan also, however, in modified forms. In particular, tectonic forces appears to be at work on the icy moon, although scientists don't see evidence of plates like on Earth.
Our system is home to about 150 moons, but Titan is exclusive in being the sole moon with a thick atmosphere. The Atmospheric pressure of its surface is about 60 percent greater than that of Earth’s. Because Titan is smaller than Earth, its gravity doesn't hold onto its gaseous envelope as tightly, therefore, the atmosphere extends to an altitude about 10 times above Earth. Titan's atmosphere mostly contains nitrogen and methane, with small amounts of other carbon-rich compounds. These molecules are split apart by the Sun's ultraviolet. Due to high atmospheric pressure, pieces of those molecules recombine to make a spread of organic chemicals including nitrogen, oxygen and other elements.
Some of the compounds produced by that splitting and recycling of methane and nitrogen creates a thick orange-coloured haze that covers the moon's surface making it difficult to look at from space. Spacecraft and telescopes can, however, see through the haze at certain wavelengths of sunshine not visible to human eyes.
A number of heavy, carbon-rich compounds settle on the moon’s surface which play the role of sand. And methane condenses into clouds that occasionally drench the surface in methane storms.
Titan
The methane in Titan’s atmosphere is what makes its complex atmospheric chemistry possible, but where all that methane comes from may be a mystery. Because sunlight continuously breaks down the methane present in the moon’s atmosphere, some source must be replenishing it or it would have depleted over time. Some researchers believe that methane might be produced by cryovolcanism. Plenty of observations by Cassini spacecraft reveal that Titan is hiding an underground ocean of liquid water. The Ecu Space Agency’s Huygens probe also measured radio signals during its descent to the surface, in 2005, that strongly suggested the presence of an ocean, 35 to 50 miles below the icy ground. This discovery adds Titan to the few worlds in our system that would potentially contain habitable environments.
Additionally, Titan’s rivers, lakes and seas of liquid methane and ethane might function a habitable environment on the moon’s surface, though any life there would likely be very different from Earth’s life. Thus, Titan could potentially harbour environments with conditions for life. Although there is so far no evidence of life on Titan, its complex chemistry and unique environments are sure to make it a destination for continued exploration.
Article by - Nehal Sharma
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